Study Of Freeze-thaw Damage Law And Early Warning Model Of Sandstone With Different Saturation

In response to the strategic instructions of China's"Western Development"and"The Belt and Road Initiative",the quality and scale of engineering construction in cold region are also increasing.In order to ensure the safety of construction and operation of rock engineering in cold region,the strength,deformation,failure law,mechanical properties and influencing factors of rock mass in cold region have become the primary research objects.Considering that water plays a decisive role in the freeze-thaw cycle of sandstone,this paper summarized the damage rule of saturation to the internal structure of freeze-thaw sandstone through the freeze-thaw cycle test and physical and mechanical properties of sandstone with different saturation.According to the thin film water theory and the capillary theory,the water molecules migration law in the freezing process is obtained.Finally,the freezing rate of different pore size is proposed according to the water molecules migration law and the ice damage theory.In order to solve the safety problem of rock engineering with different saturation under the action of freeze-thaw cycle,according to the critical slowing phenomenon of sandstone compression failure,and combined with GWO BP algorithm,a kind of early signal warning model for rock engineering failure is proposed.The following research works are carried out specifically:(1)The strength of sandstone decreases first and then increases slowly with the increase of saturation.It is found that there are two dividing points in the damage variable curve,the threshold of freezing crack after 75%saturation and the threshold of 85%saturation.For the freeze-crack threshold,the conversion rate of bound fluid and free fluid is the highest.For the saturation threshold,the bound fluid and permeability peak,allowing more free fluid to migrate through water and be absorbed by more rock particles.(2)The internal structure of sandstone is observed.According to the thin film water theory and capillary theory,the migration law of water molecules during the freezing process of sandstone is obtained.The migration direction of unfrozen water during the freezing process is as follows:micropore?mesoporous?macropore.The diffusion rate of fractures in pores with different pore sizes was analyzed by using the ice separation theory.The propagation rate of fractures under different pore sizes was obtained.The propagation rate of fractures was(1_??>(1_??>(1_??.(3)In order to solve the effect of freeze-thaw cycles on the dangers of rock engineering,based on the experiment of uniaxial compression in the process of acoustic emission signals of the phenomenon of critical slowing down,and combining the GWO-BP neural network,puts forward a model of early warning signal,to rock engineering damage failure phenomenon,early warning for cold regions engineering construction and resources development is of great significance.There are 53 Figures,15 tables and 89 references in this paper.